The present invention generally relates to power hand tools and more particularly to a rotary to reciprocating motion conversion attachment for the same.
Small rotary hand tools have been marketed for many years for use in carrying out woodworking and metal working tasks by hobbyists as well as commercial artisans. Such small rotary hand tools generally have a motor unit with a rotary output shaft that is adapted to be connected to a number of implements for doing such application work as grinding, polishing, drilling and sanding, among other tasks. Such hand tools are also configured to operate with accessories, such as, for example, a long sheathed cable to which a sanding implement or rotary cutting implement can be attached, a planing attachment as well as a right angle attachment that facilitates use of implements in special applications.
The drive unit of many recent models of such rotary hand tools is relatively small and lightweight and is capable of being easily used by a user. Such rotary hand tools may have a diameter less than about two inches and a length of only about six inches. The tool has a small but powerful electric motor that drives an output shaft at high speed and a rotary implement can be typically attached to the tool's output shaft which is axially aligned with the generally cylindrical hand tool.
While most of the applications that have been discussed above are directed to applications where rotary implements are used in various ways, there are other desirable uses for such rotary hand tools if an accessory were to be attached to the hand tool that would convert the rotary motion into reciprocating motion so that cutting, sawing sanding, filing, buffing and polishing implements that reciprocate could be used. Mechanisms which convert rotary motion to reciprocating motion are known in the art, but many have one or more disadvantages in that they may not provide a sufficiently large reciprocating stroke to be efficient and effective, or they may not be sufficiently robust to have a long useful life or exhibit sufficient cutting or sawing force during operation. The mechanisms for producing a reciprocating action for a saw blade or the like generally produce a sinusoidal movement in that the duration of a stroke in one direction is equal to the duration of the stroke in the reverse direction.
For many saw blades, such as commercially available saber saw blades, the actual cutting action that is made by the blade is in a particular direction, i.e., the cutting stroke and the other movement is a return stroke which to returns the blade to the position where the next cutting stroke begins. Since the cutting action only occurs during one-half of the total length of movement of the blade, cutting action may be optimized by having the cutting stroke be of longer duration than the return stroke. This asymmetrical timing of the two strokes does not exist in known prior art rotary to reciprocating motion conversion apparatus.